The present invention relates to antennas, specifically electronically steered antennas. In comparison with a mechanically gimbaled antenna, an electronically steered antenna is potentially more immune to critical failures (no moving parts, graceful degradation by failing components) and may more easily be constrained in dimensions. However, depending on its complexity (e.g. number of scan axes), an electronically steered antenna is typically characterized by medium to high cost. When either antenna is mounted over a large metal ground plane such as the top of a passenger airplane, close to grazing-angle antenna beams (low-elevation beams in the case of a top-mounted aircraft antenna) will be adversely affected by scattering from the platform, degrading the free-space performance of the antenna.
Several types of antennas make use of the platform body (or of a separate metal plate parallel to the platform) in order to generate a far-field beam pattern that peaks at a low elevation angle above the ground plane. Noteworthy examples include monopole antennas, blade antennas and ground-plane reflected dielectric rod antennas. These antennas are, however, non-steerable and provide fixed polarization. One notable exception is a Luneberg hemispherical lens antenna sitting on top of a metal-plane plate, as shown for example in xe2x80x9cDBS-2400 In-Flight TV Antenna Systemxe2x80x9d, Product Information Sheet, Datron/Transco Inc., 200 West Los Angeles Avenue, Simi Valley, Calif. 93065 (hereinafter DBS2400). Beam steering for this antenna is effected by mechanical rotation of its metal-plane plate in azimuth, and angular placement of a feed element in elevation. Control of the feed element polarization directly determines the antenna polarization. Gain enhancement of the DBS2400 antenna is achieved by virtue of reflection from the ground plane, as well as by the arraying of 4 Luneberg hemispherical lenses.
A Luneberg hemispherical lens may be used for the implementation of an electronically steered antenna unit by the incorporation of a switch network that selects one or a group of adjacent feed elements from a concave feed array that partially covers the hemispherical Luneberg lens. Several such antenna units (3 to 4) would be needed for full azimuth coverage, but this will not allow the arrayed combination of several hemispherical lenses for gain enhancement (DBS-2400).
There is thus a widely recognized need for, and it would be highly advantageous to have, a low-profile, cost-effective, polarization-controlled, electronically steered antenna that achieves modularly tailored high directive gain at low elevation angles above a large ground plane on top of which it is mounted.
The present invention discloses an innovative cylindrical, ray-imaging, electronically-steered array antenna, whose radiating array elements are disposed on a cylindrical surface sector above an electrically conductive ground plane that enhances the antenna gain. The conductive ground plane forms an integral part of the antenna, and the required dimensions of this ground plane depend on the array radius, and on the lowest elevation coverage angle from the (possibly tilted) ground plane. The antenna of the present invention is further characterized by a modular design that tailors the required antenna gain and azimuthal directivity through the stacking of identical antenna segments side by side. The idea is to use the multiple-beam ray focusing property of a microwave lens when feeding a circular ring array, and at the same time produce coherent ray imaging from a bottom metal plate, which, under appropriate conditions, will effectively double the antenna aperture in elevation.
According to the present invention there is provided, in a first preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of horizontally-polarized radiating arc elements and an elevation beam-forming assembly, the plurality of radiating arc elements disposed adjacently about a common axis, and an electrically conductive ground reflector plane positioned parallel to the common axis, the ground reflector plane allowing gain-enhanced, horizontal-polarization beam generation and steering in planes perpendicular to the ground reflector plane, whereby the antenna is electronically steerable in elevation, or both in elevation and in azimuth.
According to one feature of the first preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a two-dimensional semi-circular microwave lens with an internal perfect electric conductor reflector and a beam selector switching module.
According to another feature of the first preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens is a sector of a RKR-type lens.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the RKR-type lens is selected from the group consisting of stripline printed circuits, microstrip printed circuits and semi-circular parallel-plate microwave lens.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens is a sector of a two-dimensional Lunenberg-type microwave lens.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, each two-dimensional Lunenberg-type microwave lens is implemented in a configuration selected from the group consisting of a plurality of coaxial semi-rings of varying dielectric constants, a perforated dielectric disc with a radially varying density of holes, and a plurality of dielectrically loaded parallel plates with radially varying partial loading.
According to yet another feature of the first preferred embodiment of the antenna of the present invention, the beam selector switching module includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the beam selection switching module includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to the present invention, the first preferred embodiment of the antenna of the present invention further comprises a power combiner connected electrically to the outputs of at least two antenna segments, and selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to the present invention, there is provided, in a second preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of vertically-polarized radiating arc elements and an elevation beam-forming assembly, the plurality of radiating arc elements disposed adjacently about a common axis, and an electrically conductive ground reflector plane positioned parallel to the common axis, the ground reflector plane allowing gain-enhanced, vertical-polarization beam generation and steering in planes perpendicular to the ground reflector plane.
According to one feature of the second preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a two-dimensional semi-circular microwave lens with an internal perfect magnetic conductor reflector and a beam selector switching module.
According to another feature of the second preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens is a sector of a RKR-type lens.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the RKR-type lens is selected from the group consisting of stripline printed circuits, microstrip printed circuits and semi-circular parallel-plate microwave lens.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens is a sector of a two-dimensional Lunenberg-type microwave lenses.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, each two-dimensional Lunenberg-type microwave lens is implemented in a configuration selected from the group consisting of a plurality of coaxial semi-rings of varying dielectric constants, a perforated dielectric disc with a radially varying density of holes, and a plurality of dielectrically loaded parallel plates with radially varying partial loading.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the beam selector switching module includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the second preferred embodiment of the antenna of the present invention, the beam selection switching module includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to the present invention, the second preferred embodiment of the antenna of the present invention further comprises a power combiner connected electrically to the outputs of least two antenna segments, and selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to the present invention there is provided, in a third preferred embodiment, a ray-imaging, electronic beam-steering antenna comprising at least one antenna segment, each antenna segment having at least one output and including a plurality of dual-polarized radiating arc elements and an elevation beam-forming assembly, the plurality of radiating arc elements disposed adjacently along a common axis, and an electrically conductive ground reflector plane positioned parallel to the common length axis, the ground reflector plane allowing, for any polarization, gain-enhanced, beam generation and steering in planes perpendicular to the ground reflector plane.
According to one feature of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a pair of two-dimensional semi-circular microwave lenses, one of the pair having an internal perfect electric conductor reflector, and the other of the pair having an internal perfect magnetic conductor, and a pair of beam selector switching modules, connected respectively to each of the pair of two-dimensional semi-circular microwave lenses.
According to another feature of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly further includes a complex weighting module connected to the pair of beam selector switching modules.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the pair of two-dimensional semi-circular microwave lenses includes a sector of a pair of RKR-type lenses.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the pair of RKR-type lenses is selected from the group consisting of stripline printed circuits, microstrip printed circuits and semi-circular parallel-plate microwave lenses.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the pair of two-dimensional semi-circular microwave lenses includes a sector of a pair of two-dimensional Lunenberg-type microwave lenses.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each lens of the pair of two-dimensional Lunenberg-type microwave lenses is implemented in a configuration selected from the group consisting of a plurality of coaxial semi-rings of varying dielectric constants, a perforated dielectric disc with a radially varying density of holes, and a plurality of dielectrically loaded parallel plates with radially varying partial loading.
According to the present invention, the third preferred embodiment of the antenna of the present invention further comprises at least one power combiner connected electrically to the outputs of least two antenna segments, the power combiner selected from the group consisting of a conventional power combiner, a power combiner having phase shifters, a power combiner having delay phase shifters, a Ruze-type lens, a Rotman-type lens, and any combination thereof.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each of the pair of beam selector switching modules includes a single-pole switching module that incorporates a passive beam conversion matrix.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each of the pair of beam selector switching modules includes a two-pole switch module, whereby the two-pole switch module allows both single pole selection and dual pole selection.
According to another version of the third preferred embodiment of the antenna of the present invention, the elevation beam-forming assembly includes a single two-dimensional microwave lens folded about a horizontal symmetry axis, and an array of 0xc2x0/180xc2x0 hybrid couplers that feed the two-dimensional lens symmetrically, and a pair of beam selector switching modules, connected respectively to xe2x80x9csumxe2x80x9d and xe2x80x9cdifferencexe2x80x9d ports of a sub-set of the array of 0xc2x0/180xc2x0 hybrid couplers.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens includes a sector of an RKR-type lens, selected from the group consisting of stripline printed circuits, microstrip printed circuits and semi-circular parallel-plate microwave lens.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, the two-dimensional semi-circular microwave lens includes a sector of a two-dimensional Lunenberg-type microwave lens.
According to yet another feature of the third preferred embodiment of the antenna of the present invention, each of the two-dimensional Lunenberg-type microwave lenses is implemented in a configuration selected from the group consisting of a plurality of coaxial semi-rings of varying dielectric constants, a perforated dielectric disc with a radially varying density of holes, and a plurality of dielectrically loaded parallel plates with radially varying partial loading.